1. Field of the Invention
The present invention relates generally to a workpiece surface finishing machine, and more particularly to an improved finishing machine having a dual barrel structure including an upper stationary container and a lower rotary container either of which is movable up and down relative to the other. The finishing machine provides fully automatic functions which permit the finishing operations such as surface finishing, deburring and the like, and other associated operations including the charging and discharging a mass (which is a mixture of workpieces and abrasive media, which is hereinafter referred to as such) to and from the dual barrel structure, the separation of the mass into workpieces and abrasive media of the end of each cycle of the finishing operation, the return of the abrasive media for reuse, and the transfer of the finished workpieces for any subsequent process.
2. Description of the Prior Art
Usually, the conventional surface finishing machine of the type disclosed herein has a dual barrel structure used for subjecting the workpieces to the finishing process and including an upper stationary container and a lower rotary container, which contain a lot of workpieces to be finish-processed and an abrasive media. For the operation of the prior art surface finishing machine, the lower rotary container is driven for rotation, causing the mass to have a toroidal motion within the dual barrel structure. One form of such machine, as disclosed in the Japanese patent application No. 50-25678 now published after examination and the Japanese utility model registration application No. 51-62189 now published as unexamined, has a dual barrel structure the upper and lower containers of which for operation are maintained close to each other and after the operation are moved away from each other to allow the mass to be discharged, and also includes a vibrating sieve or screening device located below the lower rotary container. Another form of the machine, as disclosed in the Japanese utility model registration application No. 54-15390 now published as unexamined, includes a dual barrel structure which is capable of tilting as a whole, and a vibrating sieving device below the lower rotary container. In the latter prior art machine, the upper barrel is open at the top, and when it is tilting, the mass in the barrel is allowed to be discharged from the open top down onto the screening device. In a third form of the machine, as disclosed in the Japanese utility model registration application No. 53-26718 now published as unexamined, the lower rotary container has a central hole at the bottom through which the mass is to be discharged onto the vibrating sieve below. In any of the forms mentioned above, the size of the mass separating or sieving structure must be large enough to receive all the mass properly from the container since otherwise some workpieces and/or abrasive media would possibly escape from the sieving device. When such large size mass separating structure is used with the surface finishing machine, however, the machine main frame must be built to a size that is sufficient to accommodate the mass separating structure. In addition to this disadvantage, there is another disadvantage that when the mass is discharged onto the sieving structure after the finishing operation, it is actually observed that an extremely large amount of the mass is discharged onto the sieving structure at a time as the discharge is practically uncontrolled. This uncontrolled discharge prevents the smooth mass separation to be performed by the sieving structure that is being vibrated. It therefore requires a longer period of time to complete the separating operation for a particular lot of the mass, with the accompanying adverse effect upon the workpieces to be separated from the abrasive media. That is, since the workpieces are travelling in closely spaced relationships on the sieving path and are thus more likely to impinge against each other, they have more chances of being damaged, such as impingement marks on the surface. The abrasive media collected by the separating operation is usually returned manually to the barrel structure if it is again to be used. For the automatic return of the abrasive media, it is necessary to provide an independent return apparatus. In order to implement the fully automatic operations including the automatic return of the abrasive media, the machine must be built to an increased size, which results in an increased cost of manufacture.
For the wet-type finishing operation under wet condition which is performed by using a liquid abrasive media together with water, liquid compound solution and the like, there is also known means for preventing leaks that occur in the sliding interface between the upper stationary container and the lower rotary container from entering into the bearing box supporting therein the rotary shaft for the rotary container (as disclosed in the earlier mentioned patent application No. 50-25678). This prior art machine solves the problem of the leaks by providing a dual structure rotary container which consists of an upper rotary portion containing a mass and a lower non-rotatable portion enclosing the bottom of the upper rotary portion and adapted to provide a passage for the leaks. In accordance with this prior art machine, however, the rotary shaft which rotatably supports the rotary container must be mounted to extend through the rotary container up to the upper stationary container. This rotary shaft portion exposed in the stationary container prevents the smooth toroidal flow of the mass in the dual barrel container. Another problem is that leaks of a compound solution mixed with worn out abrasive particles remaining on the passage inside the lower non-rotatable portion of the rotary container are led to enter the bearing box along the length of the rotary shaft, which also causes an improper function of the machine. It is also observed that particles of the abrasive media leaks are easily deposited to form a solid layer. This prevents the smooth rotation of the rotary shaft, thus causing an increase in the electric current through the motor. This current increase damages the motor.